فَأَقْسَمْتُ بِالْبَيْتِ الَّذِي طَافَ حَوْلَهُ ۞ رِجَالٌ بَنَوْهُ مِنْ قُرَيْشٍ وَجُرْهُمِ
Meaning: So I swear by the House around which men have circumambulated, the men who built it from Quraysh and Jurhum.
Fa-aqsamtu is first-person singular perfect from form IV of q-s-m, “I swore.” The bāʾ in bi-l-bayt introduces the object by which the oath is sworn. Ṭāfa ḥawlahu describes circumambulation, while the pronoun in banawhu refers back to the House.
Mentioning Quraysh and Jurhum locates the oath in a revered historical and sacred setting. The oath is not decorative: it gives the praise that follows a tone of public, solemn testimony.